The present invention relates to a semiconductor device and a technology for manufacturing the same and, more particularly, to a technology which is effective when applied to a semiconductor device having a power semiconductor element.
A semiconductor element for large-power applications which can handle a power of not less than several watts is referred to as a power semiconductor element. Various power semiconductor elements have been proposed, including a transistor, a FET (Field Effect Transistor), an IGBT (Insulated Gate Bipolar Transistor), and the like. Among such power semiconductor elements, power MIS (Metal Insulator Semiconductor) FETs include a so-called vertical type and a so-called horizontal type, and are further classified into structures such as a trench-gate structure and a planar-gate structure according to the structures of their gate portions. To obtain a large power, a structure has been adopted in which, e.g., a large number of (e.g., several tens of thousands of) MISFETs in a minute pattern are coupled in parallel.
Power MISFETs are used as switching elements for DC/DC converters used in the power supply circuits of various computers such as, e.g., a desktop computer, a notebook computer, and a server. Of a DC/DC converter, reductions in the capacitances of a choke coil, an input/output, and the like and a high-speed response to a load variation are required. When a system becomes higher in frequency, a switching loss and a drive loss typically increase in a power MISFET. Because the switching loss is directly proportional to the feedback capacitance of the power MISFET and the drive loss is directly proportional to the input capacitance of the power MISFET, reductions in these capacitances are required of the power MISFET used in the DC/DC converter.
FIG. 27 shows an equivalent circuit diagram for illustrating the feedback capacitance and the input capacitance. As shown in FIG. 27, when it is assumed that Cgd represents a gate-drain capacitance, Cgs represents a gate-source capacitance, and a Cds represents a drain-source capacitance, the input capacitance Cin of the power MISFET (Q) can be expressed as Cin−Cgd+Cgs, and the feedback capacitance Cfb can be expressed as Cfb=Cgd.
Based on the result of the achieved invention, the present inventors have conducted a research on prior-art technologies in terms of element characteristics such as a lower capacitance of a power semiconductor element and a reduction in manufacturing cost. As a result of conducting the research in terms of the lower capacitance, the present inventors have extracted Japanese Unexamined Patent Publication No. 2005-57050 (Patent Document 1). The technology disclosed in Patent Document 1 generally achieves a lower capacitance with a gate peripheral structure in an active region where a power MISFET is formed, but has no description of a characteristic improvement in the outer circumferential region of the active region and a reduction in manufacturing cost.    [Patent Document 1]    Japanese Unexamined Patent Publication No. 2005-57050